Acoustically-initiated or directed responses are controlled by auditory information interacting with motor pathways. The hypothesis to be tested is that the lateral tegmentum of te midbrain and isthmus of the brainstem is intimately involved in auditory-motor functions. The specific aims of the proposed research are to investigate (1) the origin and termination of efferent axonal projections from the lateral tegmentum and (2) the organization of auditory and nonauditory afferent projections to the lateral tegmentum. To acomplish these aims a combination of experimental anatomical procedures will be used in investigating the cat and opossum brainstem--including autoradiography, retrograde transport of HRP, and double labeling with fluorescent dyes. The connection of three tegmental regions will be explored: the region of the nucleus of the brachium of the inferior colliculus, the lateral lemniscal nuclei and surrounding reticular formation, and the tegmental structures ventral and lateal to the central nucleus of the inferior colliculus. The goals are to demonstrate the organization of the lateral tegmentum and possibly its interaction with auditory-motor pathways. The proposed research offers a significant contribution to understanding midbrain auditory mechanisms.